Recording and reproducing method for optical information recording medium and optical information recording medium

ABSTRACT

Tracking control is carried out by a push-pull method or by mechanical feed at the time of recording signals, and tracking control is carried out by a phase difference tracking method at the time of reproduction. Thus, a phase change type optical disk which enables phase difference reproduction and is erasable may be realized. In a phase change type optical disk having a phase difference reproduction structure, servo mechanism at the time of reproducing signals may be stably controlled by causing the reflectance of a blank portion to be higher than the reflectance of a recording mark portion.

TECHNICAL FIELD

The present invention relates to a method for recording signals at highrecording density and reproducing the recorded signals using laser beam,and an optical information recording medium used in the method.

BACKGROUND ART

Examples of a so-called read-only optical information recording mediumfor reproduction of signals using laser beams include optical disksreferred to as a compact disk (CD), a laserdisk (LD) and a digital videodisk (DVD).

Currently, DVDs can record signals at a higher density than any otherread-only optical information recording media that are commerciallyavailable at present.

The read-only DVD is an optical disk having a diameter of 120 mm and amaximum user capacity of 4.7 GB per layer for recording. The substratecommonly is formed of a disk-shaped polycarbonate having a thickness of0.6 mm and a diameter of 120 mm.

Information signals are reproduced by irradiation of laser beams with awavelength of 650 nm or 635 nm (practically in a range of 630 nm to 670nm because of errors). A tracking servo mechanism that maintains areproduction laser beam at the center of a recorded single trackutilizes phase difference tracking error signals for reproduction of aDVD (e.g., National Technical Report Vol. 32 No. 4, August, 1986,pp.72-80) (Version 1 of DVD-ROM specification).

Examples of an optical information recording medium capable of recordingand reproducing signals using laser beam include a phase change typeoptical disk, a magneto-optical disk, an optical disk using a dyematerial or the like. Among them, in a recordable phase change typeoptical disk, a chalcogenide typically is used as a recording thin filmmaterial. Generally, the crystalline state of the recording thin filmmaterial is used as a non-recorded state. Signals are recorded byirradiating the recording thin film material with laser beam so as tomelt and quench the recording thin film material so that the materialbecomes amorphous. On the other hand, in order to erase signals, therecording thin film is irradiated with laser beams at a power lower thanthat for recording so that the recording thin film becomes crystalline.

Furthermore, for the purpose of improving the recording density of aphase change optical disk, it has been proposed to determine the diskstructure so that a phase difference between light reflected from thenon-recorded portion and light reflected from the recorded portion iscaused with respect to a wavelength λ of the reproduction laser beam(e.g., Japanese Patent Publication Nos. 2773945 and 2661293, andJapanese Laid-Open Patent Publication (Tokkai-Hei) No. 6-4900). Comparedwith a general reflectance-difference reproducing structure, the phasedifference reproducing structure provides better quality signals forreproduction even if the signals are recorded at high density.

Typically, a substrate having spiral or concentric circular groovesreferred to as guide grooves is used to obtain tracking error signalsfor recording and reproducing signals on a recordable optical disk. Morespecifically, the tracking error signals can be obtained by, forexample, a push-pull method or a 3-beam method by irradiation of thelaser beam for recording and reproduction. Alternatively, a substratewith a staggered arrangement of pits referred to as wobble pits is usedfor a tracking servo mechanism by a track wobbling method (e.g.,“Optical Disk Technology” edited by Morio Ogami, published by RadioTechnology Corp, pp86-97).

As described above, read-only DVDs can store signals a higher densitythan any other commercially available optical information recordingmedia. However, users cannot record arbitrary information in theread-only DVDs.

DISCLOSURE OF INVENTION

An object of the present invention: is to provide a recordable opticalinformation recording medium that can be reproduced by a reproducingdevice for read-only DVDs and has stable focus servo characteristics.

The characteristics required for a recordable optical informationrecording medium that can be reproduced, by a reproducing device forread-only DVDs are as follows:

1. To record signals at a physical recording density equal to that ofthe read-only DVD (bit length: 0.267 μm/bit; track pitch: 0.74 cm; andmodulation system of signals: 8/16, RLL (2,10)).

2. To obtain phase difference tracking error signals from the opticalinformation recording medium in which signals are recorded.

3. To have a reflectance equal to that of the read-only DVD.

However, regarding item 3 of the reflectance, a recording medium with alower reflectance can be used by introducing minor changes such asraising the reproduction gain of the reproducing device for DVDs,lowering circuit noise, or raising the output of reproduction laserbeam.

Another object of the present invention is to provide a method forrecording signals at a physical density equal to that of the read-onlyDVD on the optical information recording medium having theabove-described characteristics and reproducing the recorded signals.

The present invention has the following features to achieve the above-described objects.

A first feature of a method for recording and reproducing information onan optical information recording medium of the present inventionincludes the steps of irradiating an optical information recordingmedium with laser beam based on an information signal, the opticalinformation recording medium including at least a recording thin filmthat effects a phase change between an amorphous state and a crystallinestate by the irradiation of the laser beam, the recording thin filmformed on a disk-shaped substrate including guide grooves; therebyrecording a desired signal by forming a record mark on the recordingthin film while applying a tracking servo mechanism with a trackingerror signal obtained from the guide groove of the substrate; andirradiating the optical information recording medium where the recordmark is formed on the recording thin film with laser beam; therebyreproducing a signal while applying a tracking servo mechanism based ona tracking error signal obtained from the record mark.

A second feature of a method for recording and reproducing informationon an optical information recording medium of the present inventionincludes the steps of irradiating an optical information recordingmedium with laser beam based on an information signal while rotating asubstrate and moving a laser beam irradiation portion so that aninterval between recorded signals in a radial direction is constant, theoptical information recording medium including at least a recording thinfilm that effects a phase change between an amorphous state and acrystalline state by the irradiation of the laser beam, the recordingthin film formed on a disk-shaped substrate including a specularrecording region. This effects the phase change to form a record mark onthe recording thin film so that desired record signals are recorded at aconstant interval in the radial direction; the optical informationrecording medium where the record mark is formed on the recording thinfilm is irradiated with laser beams; thereby reproducing a signal whileapplying a tracking servo mechanism based on a tracking error signalobtained from the record mark.

The method for recording and reproducing information on an opticalinformation recording medium of the present invention with theabove-described features allows recording and reproduction of signals ata physical density equal to that of a read-only DVD.

A first feature of an optical information recording medium of thepresent invention includes at least a recording thin film that effects aphase change between an amorphous state and a crystalline state byirradiation of laser beams. The recording thin film is formed on adisk-shaped substrate including guide grooves having a groove depth d(nm). The groove depth d, a wavelength λ₁ (nm) of a laser beam forforming a record mark on the recording thin film based on an informationsignal and a refractive index n₁ of the substrate at the wavelength λ₁satisfy the relationship:

0.05×λ₁ /n ₁ ≦d;

the groove depth d (nm), a wavelength λ₂ (nm) of a laser beam forreproducing the record mark formed on the recording thin film and arefractive index n₂ of the substrate at the wavelength λ₂ satisfy therelationship:

d≦0.09×λ₂ /n ₂;

a phase φ₁ of light reflected from the record mark and a phase φ₂ oflight reflected from a non-record mark region with respect to a laserbeam at the wavelength λ₂ satisfy the relationship:

(2n+0.7)×π<φ₂−φ₁<(2n+1.3)×π,

where n is an integer; and

an amplitude intensity I₁ of light reflected from the record mark in theoptical information recording medium and an amplitude intensity I₂ oflight reflected from the non-record mark region with respect to anincident laser beam at the wavelength λ₂ (nm) satisfy the relationship:

I ₁ <I ₂.

A second feature of an optical information recording medium of thepresent invention includes at least a recording thin film that effects aphase change between an amorphous state and a crystalline state by theirradiation of the laser beam. The recording thin film is formed on adisk-shaped substrate. A phase φ₁ of light reflected from a record markin the optical information recording medium and a phase φ₂ of lightreflected from a non-record mark region with respect to a wavelength λ₂of the laser beam for reproducing a signal recorded on the opticalinformation recording medium satisfy the relationship:

(2n+0.7)×π<φ₂−φ₁<(2n+1.3)×π,

where n is an integer.

An amplitude intensity I₁ of light reflected from the record mark in theoptical information recording medium and an amplitude intensity I₂ oflight reflected from the non-record mark region with respect to incidentlaser beam at the wavelength λ₂ (nm) satisfy the relationship:

I ₁ <I ₂.

The optical information recording medium of the present invention withthe above-described features allows recording of signals at a densityequal to that of a read-only DVD and reproduction with a reproducingdevice for a read-only DVD and has stable focus servo characteristics.

In the above embodiment, the main elements constituting the recordingthin film preferably include Ge and Te, and a ratio of Ge to Te (Ge: Te)in atomic weight is in the range from 45:55 to 55:45.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in the radial direction schematicallyshowing a multilayer structure of an optical information recordingmedium according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view in the radial direction schematicallyshowing a multilayer structure of an optical information recordingmedium according to a second embodiment of the present invention.

FIG. 3 is a schematic drawing showing a structural example of arecording device used for recording signals on the optical informationrecording medium of the present invention.

FIG. 4 is a graph showing optical constants of compositions on the lineconnecting two compositions of GeTe and Sb₂Te₃ with respect to awavelength of 650 nm.

FIG. 5 is a graph showing optical constants of Ge—Te binary materialcompositions in the vicinity of GeTe with respect to a wavelength of 650nm.

FIG. 6 is a schematic drawing showing a structural example of arecording/reproducing device used for recording and reproducing signalson the optical information recording medium of the present invention.

FIG. 7 is a view showing an example of modulated waveforms of arecording pulse for recording signals on the optical informationrecording medium in the examples of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferable embodiments will be described with reference tothe accompanying drawings.

Embodiment 1

FIG. 1 is a cross-sectional view in the radial direction schematicallyshowing a multilayer structure of an optical information recordingmedium (optical disk) 10 according to Embodiment 1 of the presentinvention. In FIG. 1, laser beams for recording and reproduction areincident from the side of a substrate 1.

The substrate 1 is formed of a resin such as polycarbonate and PMMA,glass or the like, and a surface 8 of the substrate is covered withspiral or concentric continuous grooves (guide grooves or tracks) 9.

It is desirable that the material for protective layers 2 and 4 isstable physically and chemically, namely, has a higher melting point andsoftening temperature than the melting point of a material for arecording thin film that will be described later, and that the materialfor the protective layers 2 and 4 does not form a solid solution withthe material for a recording thin film. For example, the protectivelayers 2 and 4 are preferably formed of a dielectric such as Al₂O₃,SiO_(x), Ta₂O₅, MoO₃, WO₃, ZrO₂, ZnS, AlN_(x), BN, SiN_(x), TiN, ZrN,PbF₂, and MgF₂, or a suitable combination of these dielectrics. However,the protective layers 2 and 4 are not necessarily transparent, and theymay be formed of ZnTe or the like, which has an optical absorptivitywith respect to visible light and infrared rays. Furthermore, when theprotective layers 2 and 4 are formed of different materials, there is anadvantage in that the degree of freedom for thermal and optical designincreases. The protective layers 2 and 4 can be formed of the samematerial.

A recording thin film 3 can be formed of a material that changesreversibly between a crystalline state and.:an amorphous state byirradiation of laser beam for recording. Examples of such a materialinclude a phase change material comprising Te, In, Se or the like as amain component. Te—Sb—Ge, Te—Ge, Te—Ge—Sn, Te—Ge—Sn—Au, Sb—Se, Sb—Te,Sb—Se—Te, In—Te, In—Se, In—Se—Ti, In—Sb, In—Sb—Se, In—Se—Te are known asmain components of a phase change material. These thin films generallyare formed to have an amorphous state, but the absorption of energy suchas laser beam makes the films crystalline so that the optical constants(refractive index n and extinction coefficient k) change.

A reflective layer 5 is formed of a metal element such as Au, Al, Ni,Fe, Cr or the like, or an alloy of these metals, and serves to raise theefficiency of the light absorption of the recording thin film.

A protective substrate 7 may be a spin-coated resin, the same resinsheet as the substrate 1, a glass sheet or a metal sheet that isattached with an adhesive 6. Furthermore, two recording media can beattached with an intermediate substrate interposed therebetween or thereflective layers facing each other with an adhesive so that recording,reproduction and erasing can be performed on both sides.

Each layer of the recording thin film, the protective layer, thereflective layer or the like typically is formed by electron-beamevaporation, sputtering, ion plating, CVD, laser sputtering or the like.

Suitable selection of the thicknesses of the protective layers 2 and 4and the recording thin film 3 allows a phase difference between lightreflected from a non-recorded region (generally crystalline state) andlight reflected from a record mark region (generally amorphous state)with respect to the wavelength of laser beam for reproduction of theoptical information recording medium to be (2n+1)×π, where n is aninteger, or in the vicinity of (2n+1)×π (e.g., Japanese PatentPublication No. 2068311 and Japanese Laid-Open Patent Publication(Tokkai-Hei) No. 6-4900). This type of a so-called phase change opticaldisk with a phase difference reproduction structure is more suitable toreproduce signals recorded in high density than a general reflectancedifference reproduction type phase change optical disk. Furthermore,since recorded information signals can be reproduced by utilizing thephase difference, phase difference tracking error signals can bedetected. In other words, it is possible in theory to apply a phasedifference servo tracking mechanism.

When effects of guide grooves need not be considered because there is noguide groove or the depth of the guide grooves is small, the mostdesirable phase difference for phase difference reproduction is(2n+1)×π, where n is an integer. In practice, when the wavelength of thelaser beam used is λ₂ and a groove depth d is in the range:d≦0.09×λ₂/n₂, a reproduction signal amplitude of not less than 60% ofthe ideal level and good phase difference tracking error signals can beobtained, as long as the following relationships are satisfied:

(2n+0.7)×π<φ₂−φ₁<(2n+1.3)×π,

where n is an integer: and

I ₂ /I ₁<3, more preferably, I ₂ /I ₁<2,

where φ₁ represents a phase of light reflected from the amorphous regionof the recording thin film, φ₂ represents a phase of light reflectedfrom the crystalline region of the recording thin film, I₁ represents anamplitude intensity of light reflected from the amorphous region of therecording thin film, and I₂ represents an amplitude intensity of lightreflected from the crystalline region of the recording thin film.

When the groove depth d of the guide groove substantially satisfiesd=0.07×λ₂/n₂, an ideal phase difference for recording information on thegroove is:

φ₂−φ₁=(2n−0.9)×π,

where n is an integer, and an ideal phase difference for recordingbetween the grooves is:

φ₂φ₁=(2n+0.9)×π,

where n is an integer.

The reason why the smaller ratio of the amplitude intensity I₂/I₁ isbetter is described in Japanese Laid-Open Patent Publication No. 6-4900in detail.

However, in practice, in an attempt of achieving a phase differencereproduction structure in a phase change optical disk, it is difficultto obtain a structure with a high reflectance especially with respect toa wavelength of 650 nm for reproduction light (wavelength forreproduction light specified by the DVD specification). As describedlater, the highest reflectance of a phase difference reproduction mediumthat can he achieved with a currently known chalcogen material is nomore than the 10% range. In this case, unless reproduction is performedwith an ideal reproduction drive (i.e., a drive with sufficiently lowcircuit noise and reproduction light noise), the focus servo mechanismbecomes unstable or circuit noise overlaps reproduction signals, so thatreproduction jitter values are degraded. As a result, inherentcharacteristics of the optical disk cannot be presented. Therefore, whensuch an ideal reproduction drive is not used for reproduction (forexample, a reproduction drive having worse servo characteristics thanideal levels, a reproduction drive having higher circuit noise thanideal levels or an inexpensive reproduction drive is used), goodreproduction characteristics can be obtained by designing the opticalcharacteristics of the optical disk with an emphasis on a high averagereflection even at the expense of other characteristics. In order toraise an average reflection, the reflectance in regions other than therecord marks may be raised. In this case, the reflectance in the recordmarks becomes low as a natural consequence. In other words, in thedesign of a phase difference reproduction structure, a larger ratio ofthe amplitude intensities I₂/I₁ with respect to the wavelength of thereproduction light results in a larger acceptability of the reproductiondrive to the servo characteristics. In order to have evidently betterservo characteristics during reproduction than in the case where I₁=I₂,at least the ratio of the amplitude intensities I₂/I₁ was required to belarger than 1.3.

Even in the phase change optical disk with a phase differencereproduction structure, phase difference tracking error signals cannotbe obtained in a non-recorded state. Therefore, for recording in anon-recorded region of an optical disk, a push-pull tracking method isadopted with guide grooves.

When recording is performed with the tracking servo mechanism by thepush-pull tracking method, the largest tracking error signal can beobtained when the relationship between the groove depth d (nm) of theguide groove and the wavelength λ₁ (nm) of laser beam for recording isd=0.125×λ₁/n₁, where n₁ is an refractive index of the substrate (e.g.,“Optical Disk Technology” edited by Morio Ogami, published by RadioTechnology Corp., p.87). Thus, a value in the vicinity of 0.125×λ₁/n₁ isselected as the groove depth d for a general phase change optical disk.

However, when the tracking servo mechanism is applied by the push-pullmethod using the guide grooves for recording and the tracking servomechanism is applied using phase difference tracking error signalsobtained from recorded signals for reproduction, the groove depth d ofthe guide groove is required to be examined from another point of view.

For example, when the groove depth of the guide groove is 0.125×λ₂/n₂,(where λ₂ is a wavelength of laser beam for reproduction, and n₂ is therefractive index of the substrate corresponding to the wavelength λ₂,which apply to those described later), troubles occur duringreproduction. The reason is as follows: In the case of the phasedifference reproduction, the smaller the depth of the guide groove is,the higher the quality of reproduction signals is. On the other hand,the reproduction signal is smallest when the depth d is in the vicinityof 0.125×λ₂/n₂ in principle.

Therefore, the relationship between the groove depth in the push-pullmethod and the amplitude of the tracking error signal was examined. As aresult, in the case where parameters other than the groove depth werethe same, when the groove depth was 0.05×λ₁/n₁, the amplitude of thetracking error signal was about 50% of the amplitude of a signal in anideal state (the groove depth is about 0.125×λ₁/n₁), which was found tobe the lowest limit necessary to apply the tracking servo mechanism. Inother words, in view of the traching servo for recording, the groovedepth is preferably 0.05×λ₁/n₁ or more.

Next, the relationships between the groove depth and the amplitude ofthe reproduction signal and the amplitude of the phase differencetracking error signal for phase difference reproduction of an opticaldisk where signals were recorded were examined. As a result, in the casewhere parameters other than the groove depth were the same, when thegroove depth was more than 0.09×λ₂/n₂, the qualities of the reproductionsignal and the tracking error signal were degraded so significantly thatit is difficult to put the medium to practical use. Therefore, in viewof the tracking servo characteristics during reproduction, the groovedepth is preferably 0.09×λ₂/n₂ or less.

When the relationship of λ₁ and λ₂ is λ₁<λ₂, the range of the groovedepth that satisfies the above-described relative equation is widened.In addition, for recording signals in high density, also in view ofwidening the power tolerance of recording, it is more desirable to havethe wavelength of laser beam for recording be shorter than thewavelength of laser beam for reproduction than the case of vice versa.Therefore, a preferable relationship of λ₁ and λ₂ is λ₁≦λ₂.

The relationship between a phase φ₁ of light reflected from record marksand a phase φ₂ of light reflected from non-record mark regions betweenthe record marks with respect to incident laser beam for reproductionuniquely determines whether to record signals on the grooves or betweenthe grooves. In other words, when

(2n+0.5)×π<φ₂−φ₁<(2n+1)×π

(where n is an integer), signals are recorded between the grooves in thesubstrate. When

(2n+0.5)×π<φ₂−φ₁<(2n+1.5)×π

(where n is an integer), signals are recorded on the grooves in thesubstrate. If this selection is the other way around, the obtainedamplitude of the reproduction signals becomes smaller than in the caseof the right selection. This is caused by the effect of the phasedifference resulting from the presence of the guide grooves.

The first embodiment that has been described so far assumes that therecord marks correspond to the amorphous regions in the recording thinfilm, and the non-recorded portions (also referred to as non-recordmarks) corresponds to the crystalline regions. However, the record marksmay be crystalline regions in the recording thin film, and thenon-recorded portions (non-record marks) may be amorphous regions. Inthis case, it is not necessary to initialize the optical disk(crystallize the entire recording region).

Furthermore, a recording device and a reproducing device are preferablyintegrated to form one apparatus, especially in such a manner that amechanism for rotating a disk is used for recording and reproduction.However, the recording device and the reproducing device can be usedseparately. For example, it is practical to use a commercially availableDVD reproducing apparatus or a slightly modified commercially availableDVD reproducing apparatus (for example, the reproduction gain is raised,or the intensity of reproduction light is raised so that the reproducingapparatus can be used with an optical information medium having a lowreflectance) as the reproducing device.

Tracking during recording is not limited to the push-pull method, andother systems using tracking error signals obtained from the guidegrooves, for example, a 3-beam method, can be used to obtain the sameadvantages. One application of the present invention can be as anauthoring tool of a DVD.

Embodiment 2

Next, a second embodiment of the present invention will be described.

FIG. 2 is a cross-sectional view in the radial direction showing aschematic laminated structure of an optical information recording medium(optical disk) 20 according to the second embodiment of the presentinvention. The fundamental difference from the optical disk of FIG. 1lies in that a substrate surface 18 as a recording region in a substrate11 is optically specular and no guide grooves are formed thereon. Otheraspects (e.g., phase difference reproduction structure or the like) arethe same as those of FIG. 1. More specifically, the substrate 11, aprotective layer 12, a recording thin film 13, a protective layer 14, areflective layer 15, an adhesive 16, a protective substrate 17correspond to the substrate 1, the protective layer 2, the recordingthin film 3, the protective layer 4, the reflective layer 5, theadhesive 6, and the protective substrate 7 in the first embodiment,respectively. These components will not be described in detail.

In this embodiment, the substrate includes no guide groove. Therefore,the most satisfactory phase difference signals for reproduction can beobtained when the relationship between a phase φ₁ of light reflectedfrom the recording thin film region in an amorphous state and a phase φ₂of light reflected from the recording thin film region in a crystallinestate is:

φ₂−φ₁=(2n±1)×π,

where n is an integer.

In practice, as long as the following relationships are satisfied, areproduction signal amplitude of not less than 60% of the ideal levelsand satisfactory phase difference tracking error signals can beobtained:

(2n+0.7)×π<φ₂−φ₁<(2n+1.3)×π,

(n is an integer),

where φ₁ is a phase of light reflected from the recording thin filmregion in the amorphous state, and φ₂ is a phase of light reflected fromthe recording thin film region in the crystalline state, with respect toincident laser beams at a wavelength λ₂, and

I ₂ /I ₁<3,

where I₁ is an amplitude intensity of light reflected from the recordingthin film region in the amorphous state, and I₂ is an amplitudeintensity of light reflected from the recording thin film region in thecrystalline state. The reason why a larger ratio of the amplitudeintensities I₁/I₂ is preferable is described in Japanese Laid-OpenPatent Publication No. 6-4900, which has been referred to earlier.

However, in practice, in an attempt to achieve a phase differencereproduction structure in a phase change optical disk, it is difficultto obtain a structure with a high reflectance, especially with respectto a wavelength for 650 nm for reproduction light (the wavelength forreproduction light specified by the DVD specification). As describedlater, the highest reflectance of a phase difference reproduction mediumthat can be achieved with a currently known chalcogen material is nomore than,,the 10% range. In this case, unless reproduction is performedwith an ideal reproduction drive (i.e., a drive with sufficiently lowcircuit noise and reproduction light noise), the focus servo mechanismbecomes unstable or circuit noise overlaps reproduction signals, so thatreproduction jitter values are degraded. As a result, inherentcharacteristics of the optical disk cannot be presented. Therefore, whensuch an ideal reproduction drive is not used for reproduction (forexample, a reproduction drive having worse servo characteristics thanideal levels, a reproduction drive having higher circuit noise thanideal levels or an inexpensive reproduction drive is used), goodreproduction characteristics can be obtained by designing the opticalcharacteristics of the optical disk with an emphasis on a high averagereflection even at the expense of other characteristics. In order toraise an average reflection, the reflectance in regions other than therecord marks may be raised. In this case, the reflectance in the recordmarks becomes low as a natural consequence. In other words, in thedesign of a phase difference reproduction structure, a larger ratio ofthe amplitude intensities I₂/I₁ with respect to the wavelength of thereproduction light results in a larger acceptability of the reproductiondrive to the servo characteristics. In order to have evidently betterservo characteristics during reproduction than in the case where I₁=I₂,at least the ratio of the amplitude intensities I₂/I₁ was required to belarger than 1.3.

In order to record signals on the optical information recording mediumof the present invention, for example, a recording device shown in FIG.3 can be used. A phase change optical disk 21 in a phase differencereproduction structure is secured onto a spindle motor 22 and rotatedwhile controlling the rotation. A modulated laser beam is radiated fromlaser beam source 24 in response to a signal from a signal generationcircuit 23. The laser beam is refracted at a mirror 26 provided in afeeding mechanism 25 and focused on a recording thin film by anobjective lens 27 so that information is recorded. In this case, themovement rate of the feeding mechanism 25 is controlled so that theinterval between recorded signal tracks is constant. For example, whensignals are recorded in the same density as that of a read-only DVD, thefeeding rate in the radial direction is controlled so that the intervalbetween signal tracks is about 0.74 μm. In this case, the laser beamsource 24 used for recording may be a gas laser such as an Ar laser or asemiconductor laser. A focus servo mechanism 28 may be performed with aHe—Ne laser.

The optical disk with signals recorded in this manner is irradiated witha laser beam for reproduction so that phase difference tracking errorsignals can be obtained. The tracking error signals are used for thetracking servo mechanism so that phase difference reproduction signalscan be detected.

Furthermore, for recording signals in high density, in view of wideningthe power tolerance for recording, it is more desirable to have thewavelength of the laser beam for recording be shorter than thewavelength of laser beam for reproduction rather than vice versa.Therefore, a preferable relationship of λ₁ and λ₂ is λ₁≦λ₂.

Next, the results of the examination for a preferable material for arecording thin film to obtain a phase difference reproduction structurein a phase change disk will be described below.

A general material for a recording thin film of a recordable anderasable phase change optical disk is a ternary composition of Ge—Sb—Te.Among the ternary composition based-materials, compositions having arelatively high crystallization rate are in a range centering on theline connecting the two compositions GeTe and Sb₂Te₃. The compositionswithin this range have been in practical use for the recording thinfilms of phase change optical disks.

FIG. 4 shows the results of the investigation of the optical constantsat a wavelength of 650 nm in the amorphous state and the crystallinestate with respect to the compositions on the line connecting twocompositions GeTe and Sb₂Te₃. In the vertical axis of FIG. 4, nrepresents a refractive index, and k represents an extinctioncoefficient. As seen from FIG. 4, the change in the optical constant islarger as the composition is closer to GeTe. In an attempt to obtain aphase difference reproduction structure in a phase change optical disk,a larger change in the optical constant between the amorphous state andthe crystalline state results in a higher reflectance in the structure.

The structures are formed with a substrate composed of polycarbonate, a10 nm recording thin film, protective layers both at the substrate sideand the reflective layer side composed of a transparent dielectric(supposedly ZnS-20 mol % of SiO₂) having a refractive index of 2.1, anda 50 nm reflective layer composed of Au. In this case, among thestructures that have a phase difference π between the light reflectedfrom the amorphous portions and the light reflected from the crystallineportions with respect to incident light at a wavelength of 650 nm, thestructures having a reflectance of the former equal to that of thelatter and the largest reflectance were determined by opticalcalculation. Table 1 shows the results.

TABLE 1 Ge content (at %) 15 20 25 30 35 40 45 50 Reflectance (%) 3 4 56 7 9 10 11

As seen from Table 1, the recording thin film whose composition iscloser to GeTe has a higher reflectance. This tendency is presented withrecording thin films having different thicknesses. However, when thethickness of the recording thin film is less than 5 nm or more than 20nm, the reflectance of the recording thin film having a phase differenceπ is excessively low or substantially nil, so that it is difficult toput the medium to practical use.

In the case of the optical disk of this embodiment, the higherreflectance is the more preferable. This is because the reflectancebecomes closer to the reflectance of a read-only optical disk. Then, thecompositions in the vicinity of GeTe in a binary composition of Ge—Tewere examined. FIG. 5 shows the results. In the vertical axis of FIG. 5,n represents a refractive index, and k represents an extinctioncoefficient. As seen from FIG. 5, the change in the optical constant isthe largest in the composition in the vicinity of Ge₅₃Te₄₇ (thecomposition ratio is expressed by the ratio in atomic weight).

The structures were formed with a substrate composed of polycarbonate, a10 nm recording thin film, protective layers both at the substrate sideand the reflective layer side composed of a transparent dielectric(supposedly ZnS-20 mol % of SiO₂) having a refractive index of 2.1, anda 50 nm reflective layer composed of Au. In this case, among thestructures that have a phase difference π between the light reflectedfrom the amorphous portions and the light reflected from the crystallineportions with respect to incident light at a wavelength of 650 nm, thestructures having a reflectance of the former equal to that of thelatter and the largest reflectance were determined by opticalcalculations. Table 2 shows the results.

TABLE 2 Ge content (at %) 42.5 45.0 47.5 50.0 52.5 55.0 57.5 Reflectance(%) 6 9 10 11 12 10 7

As seen from Table 2, the recording thin film whose composition is inthe vicinity of Ge₅₃Te₄₇ (the composition ratio is expressed by theratio in atomic weight) has the highest reflectance. Furthermore, whenthe Ge content is from 45 at % to 55 at %, the obtained phase differencereproduction structure can perform well at the wavelength of 650 nm forreproduction light. This tendency is presented with recording thin filmshaving different thicknesses. However, when the thickness of therecording thin film is less than 5 nm or more than 20 nm, thereflectance of the recording thin film having a phase difference of π isexcessively low or substantially nil, so that it is difficult to put themedium to practical use.

As described above, it is preferable that the main elements constitutingthe recording thin film are Ge and Te, and that the ratio in the atomicweight of Ge to Te is in the range from 45:55 to 55:45. Herein, “mainelement” refers to an element that has a relatively high ratio in theatomic weight among the elements constituting the recording thin film.The phrase “the main elements are Ge and Te” means that the elementsthat have the highest and the second highest ratio in the atomic weightamong the elements constituting the recording thin film are Ge and Te.

Thus, optically, when a recording thin film is composed of a Ge—Tematerial containing Ge in the range from 45 at % to 55 at %, morepreferably, a composition in the vicinity of Ge₅₃Te₄₇, a phasedifference reproduction medium having a higher reflectance can beobtained.

However, when selecting a recording thin film material, in addition tothe optical characteristics, it is important to make sure that thematerial has a crystallization rate corresponding to the recordinglinear velocity. According to the results of this examination, when therecording linear velocity was in the range from 2.6 m/s to 8 m/s, andthe Ge content was 52 at % to 55 at % or 45 at % to 48 at %,satisfactory record marks were formed.

Furthermore, other elements were added to a Ge—Te binary alloy in orderto improve the reproduction optical degradation characteristics byraising the temperature for crystallization of the recording thin film.As a result, the characteristics were improved by adding at least oneselected from the group consisting of rare gas elements, B, C, Al, Si,Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Ni, Se, Nb, Sb, Ta, W, Au, Pb and Bi inan appropriate amount.

However, when the atomic weight of an element other than Ge and Te amongthe above-listed elements was more than 10% of the sum of the atomicweights of Ge and Te, the change in the, optical characteristics becamesmall. Thus, a large reflectance was not obtained in some cases.Therefore, these elements are added preferably in an amount not morethan 10% of the sum of the atomic weights of Ge and Te.

The composition of the recording thin film described above can beapplied as the recording thin film of the optical information recordingmedium according to the first embodiment of the present invention.

The second embodiment that has been described so far assumes that therecord marks correspond to the amorphous regions in the recording thinfilm, and the non-recorded portions (non-record marks) correspond tocrystalline regions. However, the record marks may be crystallineregions in the recording thin film, and the non-recorded portions(non-record marks) can be amorphous regions. In this case, it is notnecessary to initialize the optical disk (crystallize the entirerecording region).

Furthermore, a recording device and a reproducing device preferably areintegrated to form one apparatus, especially in such a manner that amechanism for rotating a disk is used for recording and reproduction.However, the recording device and the reproducing device may be usedseparately. For example, it is practical to use a commercially availableDVD reproducing apparatus or a slightly modified commercially availableDVD reproducing apparatus (for example, the reproduction gain is raised,or the intensity of reproduction light is raised so that the reproducingapparatus can be used with an optical information medium having a lowreflectance) as the reproducing device. One application of the presentinvention can be as an authoring tool of a DVD. However, the presentinvention is not limited to the read-only DVD. The present inventionprovides a recording and reproducing method and an optical informationrecording medium useful in a higher density recording format.

Hereinafter, the present invention will be described more specificallyby way of specific examples.

EXAMPLE 1

ZnS—SiO₂, Ge₅₃Te₄₇, ZnS—SiO₂, and Au films were sequentially formed inthicknesses of 70 to 140 nm, 10 nm, 39 nm, and 50 nm, respectively, on asubstrate composed of polycarbonate having a diameter of 120 mm and athickness of 0.6 mm by magnetron sputtering. The surface of thesubstrate was covered with guide grooves forming concavities andconvexities having a pitch of 0.74 μm and a groove depth of 26 nm. Apolycarbonate substrate with the same shape was attached to the obtainedoptical disk with an ultraviolet curing resin to act as a back cover(protective substrate). The refractive index of the polycarbonatesubstrate was 1.59 at a wavelength of 650 nm. The opticalcharacteristics of this optical disk with respect to a wavelength of 650nm were measured (the optical characteristics were measured by using aspecular substrate that includes no guide grooves in order to avoid theinfluence of diffraction at the grooves). When the thickness of theZnS—SiO₂ layer on the side of the substrate was 104 nm, the reflectanceof the recording thin film in the amorphous state and the reflectance ofthe recording thin film in the crystalline state were both 10%. Thereflectance in the crystalline state becomes higher, whereas thereflectance in the amorphous state becomes lower, as the thickness ofthe ZnS—SiO₂ layer on the side of the substrate is smaller than 104 nm.In this case, the phase difference between the reflected light in thecrystalline state and the reflected light in the amorphous state is0.9π, which is common to all the disks. This is because the phasedifference primarily depends on the thickness of the ZnS—SiO₂ layer onthe side of the reflective layer. The phase difference between thereflected light in the crystalline state and the reflected light in theamorphous state was measured with an interference microscope. Theseoptical disks were initialized. The crystalline state of the recordinglayer corresponded to the non-recorded state, and the amorphous state ofthe recording layer corresponded to the record marks.

Signals were recorded on these optical disks and the recorded signalswere reproduced with a recording and reproducing device as shown in FIG.6. An optical disk 29 was secured onto a spindle motor 30 and rotatedtherewith while controlling the rotation. Signals were recorded byfocusing a laser beam radiated from a laser beam source 31 on therecording thin film by an objective lens 32. The signals were reproducedby detecting the laser beam radiated from the laser beam source 31through the objective lens 32 and a half mirror 33 by a photodetector34. In FIG. 6, reference numeral 35 denotes a tracking servo mechanism,and reference numeral 36 denotes a focus servo mechanism.

The laser beam source 31 used for the recording and the reproduction isa semiconductor laser with wavelength of 650 nm. The NA (numericalaperture) of the objective lens 32 is 0.6. In the process of therecording, a push-pull method was used for tracking, and the signalswere recorded between the guide grooves.

FIG. 7 shows modulated waveforms of a recording pulse. Information forrecording was recorded with pulses modulated in a 8/16, RLL (2,10)modulation system. At this time, the recording linear velocity was 3.5m/s, and the linear density of recorded signals was 0.267 μm/bit. Whenthe recording pulse duty was 30%, signals were able to be recorded witha peak power of 7.1 mW. For reproducing the recorded signals, phasedifference tracking error signals were detected and used for thetracking servo mechanism. The power of the reproduction light was 0.8mW.

Table 3 shows reproduction jitter s for each disk when the drive isswitched between two states. In a first drive state, circuit noise ofreproduction system is reduced as much as possible. In a second drivestate, noise is intentionally caused in the circuit of the reproductionsystem.

TABLE 3 State 1 (circuit noise:low) State 2 (circuit noise:high)Reflectance Repro- Reproduction Repro- Reproduction Ratio ductionwaveform duction waveform I₂/I₁ jitter envelope jitter envelope4.0 >25%   good >25%   good 3.0 14% good 16% good 2.0 12% good 13% good1.3 10% good 14% good 1.0  9% good 20% disturbed

A high reflectance ratio of a disk in Table 3 means that the disk has ahigh initial reflectance ratio and a high average reproductionreflectance after recording. When the reflectance ratio is high,satisfactory reproduction jitters can be obtained, partly because astable focus servo operation can be obtained even in a high noisereproduction system. However, when the reflectance ratio is excessivelyhigh (more than 3), the signal quality for phase difference reproductionis degraded before considering the stability of reproduction, so thatreproduction jitters are degraded.

When signals were recorded on the guide grooves, the reproductionjitters were larger under any recording conditions than those obtainedwhen signals were recorded between the guide grooves.

In this example, the crystalline state of the recording thin film wasused as an initial state (non-recorded state). However, when acrystallization treatment was not performed and the amorphous state wasused as the non-recorded state, and recording was performed bycrystallization, the same results as those of Table 3 were obtained.

EXAMPLE 2

ZnS—SiO₂, Ge₅₃Te₄₇, ZnS—SiO₂, and Au films were sequentially formed inthicknesses of 70 to 140 nm, 10 nm, 48 nm, and 50 nm, respectively, on asubstrate composed of polycarbonate having a diameter of 120 mm and athickness of 0.6 mm by magnetron sputtering. The surface of thesubstrate was covered with guide grooves forming concavities andconvexities having a pitch of 0.74 μm and a groove depth of 26 nm. Apolycarbonate substrate with the same shape was attached to the obtainedoptical disk with an ultraviolet curing resin to act as a back cover(protective substrate). The refractive index of the polycarbonatesubstrate was 1.59 at a wavelength of 650 nm. The opticalcharacteristics of this optical disk with respect to a wavelength of 650nm were measured (the optical characteristics were measured by using aspecular substrate that includes no guide grooves in order to avoid theinfluence of diffraction at the grooves). When the thickness of theZnS—SiO₂ layer on the side of the substrate was 104 nm, the reflectanceof the recording thin film in the amorphous state and the reflectance ofthe recording thin film in the crystalline state were both 10%. Thereflectance in the crystalline state becomes higher, whereas thereflectance in the amorphous state becomes lower, as the thickness ofthe ZnS—SiO₂, layer on the side of the substrate is smaller than 104 nm.In this case, the phase difference between the reflected light in thecrystalline state and the reflected light in the amorphous state is1.1π((2-0.9)×π in another expression), which is common to all the disks.This is because the phase difference primarily depends on the thicknessof the ZnS—SiO₂ layer on the side of the reflective layer. The phasedifference between the reflected light in the crystalline state and thereflected light in the amorphous state was measured with an interferencemicroscope. These optical disks were initialized. The crystalline stateof the recording layer corresponded to the non-recorded state, and theamorphous state of the recording layer corresponded to the record marks.

Signals were recorded on these optical disks and the recorded signalswere reproduced with a recording and reproducing device as shown in FIG.6. The laser beam source used for recording and reproduction is asemiconductor laser with wavelength of 650 nm. The NA (numericalaperture) of the objective lens is 0.6. In the process of the recording,a push-pull method was used for tracking, and the signals were recordedon the guide grooves.

FIG. 7 shows modulated waveforms of a recording pulse. Information forrecording was recorded with pulses modulated in a 8/16, RLL (2,10)modulation system. At this time, the recording linear velocity was 3.5m/s, and the linear density of recorded signals was 0.267 μm/bit. Whenthe recording pulse duty was 30%, signals were able to be recorded witha peak power of 7.1 mW. For reproducing the recorded signals, phasedifference tracking error signals were detected and used for thetracking servo mechanism. The power of the reproduction light was 0.8mW.

Table 4 shows reproduction jitters for each disk when the drive isswitched between two states. In a first drive state, circuit noise ofthe reproduction system is reduced as much as possible. In a seconddrive state, noise is intentionally caused in the circuit of thereproduction system.

TABLE 4 State 1 (circuit noise:low) State 2 (circuit noise:high)Reflectance Repro- Reproduction Repro- Reproduction Ratio ductionwaveform duction waveform I₂/I₁ jitter envelope jitter envelope4.0 >25%   good >25%   good 3.0 15% good 16% good 2.0 12% good 13% good1.3 10% good 13% good 1.0  9% good 22% disturbed

A high reflectance ratio of a disk in Table 4 means that the disk has ahigh initial reflectance ratio and a high average reproductionreflectance after recording. When the reflectance ratio is high,satisfactory reproduction jitters can be obtained, partly because astable focus servo operation can be obtained even in a high noisereproduction system. However, when the reflectance ratio is excessivelyhigh (more than 3), the signal quality for phase difference reproductionis degraded before considering the stability of reproduction, so thatreproduction jitters are degraded.

When signals were recorded between the guide grooves, the reproductionjitters were larger under any recording conditions than those obtainedwhen signals were recorded on the guide grooves.

In this example, the crystalline state of the recording thin film wasused as an initial state (non-recorded state). However, when acrystallization treatment was not performed and the amorphous state wasused as the non-recorded state, and recording was performed bycrystallization, the same results as those of Table 4 were obtained.

EXAMPLE 3

ZnS—SiO₂, Ge₅₃Te₄₇, ZnS—SiO₂, and Au films were sequentially formed inthicknesses of 70 to 140 nm, 10 nm, 44 nm, and 50 nm, respectively, on asubstrate composed of polycarbonate having a diameter of 120 mm and athickness of 0.6 mm by magnetron sputtering. The surface of thesubstrate for the recording region was specular. A polycarbonatesubstrate with the same shape was attached to the obtained!optical diskwith an ultraviolet curing resin to act as a back cover (protectivesubstrate). The optical characteristics of this optical disk withrespect to a wavelength of 650 nm were measured. When the thickness ofthe ZrS—SiO₂ layer on the side of the substrate was 104 nm, thereflectance of the recording thin film in the amorphous state and thereflectance of the recording thin film in the crystalline state wereboth 10%. The reflectance in the crystalline state becomes higher,whereas the reflectance in the amorphous state becomes lower, as thethickness of the ZnS—SiO₂ layer on the side of the substrate is smallerthan 104 nm. In this case, the phase difference between the reflectedlight in the crystalline state and the reflected light in the amorphousstate is 1.0π, which is common to all the disks. This is because thephase difference primarily depends on the thickness of the ZnS—SiO₂layer on the side of the reflective layer. The phase difference betweenthe reflected light in the crystalline state and the reflected light inthe amorphous state was measured with an interference microscope. Theseoptical disks were initialized. The crystalline state of the recordinglayer corresponded to the non-recorded state, and the amorphous state ofthe recording layer corresponded to the record marks.

Signals were recorded on these optical disks with a recording device asshown in FIG. 3. The laser beam source used for recording is asemiconductor laser with wavelength of 65 nm. The NA (numericalaperture) of the objective lens is 0.6. In the process of recording, thefeeding rate in the radial direction of the objective lens wascontrolled so that the interval between signal tracks was about 0.74 μmconstantly. FIG. 7 shows modulated waveforms of the recording pulse.Information for recording was recorded with pulses modulated in a 8/16,RLL (2,10) modulation system. At this time, the recording linearvelocity was. 3.5 m/s, the linear density of recorded signals was 0.267μm/bit. When the recording pulse duty was 30%, signals were able to berecorded with a peak power of 6.9 mW.

For reproducing the recorded signals, a recording and reproducing deviceas shown in FIG. 6 was used. The laser beam source is a semiconductorlaser with wavelength of 650 nm. The NA (numerical aperture) of theobjective lens is 0.6. Phase difference tracking error signals weredetected and used for the tracking servo mechanism. The power of thereproduction light was 0.8 mW. Then, the reproduction characteristics ofthe disks were compared in the reproduction drive where the circuitnoise was reduced as much as possible and in the reproduction drivewhere the noise was raised intentionally. The results were as follows.When the reflectance ratio I₂/I₁ was 1.3 or more with respect to thewavelength (650 nm) of the reproduction light, the stability duringreproduction, especially the stability of the focus servo mechanism, wasraised and satisfactory reproduction jitters were obtained. On the otherhand, in the disks having a reflectance ratio I₂/I₁ of more than 3,although the focus servo mechanism was stabilized, the quality of phasedifference reproduction signals, which is more important, was degraded.

EXAMPLE 4

Signals were recorded on the same optical disk as in Example 3 with arecording device as shown in FIG. 3. The laser beam source used forrecording is an Ar laser with wavelength of 458 nm. The NA (numericalaperture) of the objective lens is 0.55. In the process of recording,the feeding rate in the radial direction of the objective lens wascontrolled so that the interval between signal tracks was about 0.74 μmconstantly. FIG. 7 shows modulated waveforms of the recording pulse.Information for recording was recorded with pulses modulated in a 8/16,RLL (2,10) modulation system. At this time, the recording linearvelocity was 3.5m/s, the linear density of recorded signals was 0.267μm/bit. When the recording pulse duty was 30%, signals were able to berecorded with a peak power of 7.3 mW.

For reproducing the recorded signals, a recording and reproducing deviceas shown in FIG. 6 was used. The laser beam source is a semiconductorlaser with wavelength of 650 nm. The NA (numerical aperture) of theobjective lens is 0.6. Phase difference tracking error signals weredetected and used for the tracking servo mechanism. The power of thereproduction light was 0.8 mW.

The jitter of the reproduction signals was 1 to 2% better than that ofthe same disk in Example 3. As in Example 3, when the reflectance ratioI₂/I₁ was 1.3 or more at 650 nm of the reproduction light, the stabilityduring reproduction, especially the stability of the focus servomechanism, was raised and satisfactory reproduction jitters wereobtained. On the other hand, in the disks having a reflectance ratioI₂/I₁ of more than 3, although the focus servo mechanism was stabilized,the quality of phase difference reproduction signals, which is moreimportant, was degraded.

The embodiments and the examples disclosed in this application areintended to describe the technical idea of the present invention and areto be considered as illustrative and not limiting the present invention.The present invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof and the scope ofthe invention, and all changes which come within the meaning and rangeof equivalency of the claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The present invention can be utilized in a variety of recordable opticaldisks such as a phase change optical disk, a magneto-optical disk and adye disk, and an apparatus for recording and reproducing information onthese optical disks.

What is claimed is:
 1. A method for recording and reproducinginformation on an optical information recording medium, comprising thesteps of: irradiating an optical information recording medium with alaser beam based on an information signal, the optical informationrecording medium comprising at least a recording thin film that effectsa phase change between an amorphous state and a crystalline state by theirradiation of the laser beam, the recording thin film formed on adisk-shaped substrate including guide grooves; thereby recording adesired signal by forming a record mark on the recording thin film whileapplying a tracking servo mechanism with a tracking error signalobtained from the guide grooves of the substrate; and irradiating theoptical information recording medium where the record mark is formed onthe recording thin film with laser beam; thereby reproducing a signalwhile applying a tracking servo mechanism based on a tracking errorsignal obtained from the record mark; wherein a groove depth d (nm) ofthe guide groove, a wavelength λ₁ (nm) of the laser beam for recordingand a refractive index n₁ of the substrate at the wavelength λ₁ satisfya relationship: 0.05×λ₁ /n ₁ ≦d; a groove depth d (nm) of the guidegroove, a wavelength λ₂ (nm) of the laser beam for reproducing therecord mark formed on the recording thin film and a refractive index n₂of the substrate at the wavelength λ₂ satisfy a relationship: d≦0.09×λ₂/n ₂; and the wavelength λ₂ and the wavelength λ₁ satisfy arelationship: λ₁≦λ₂.
 2. The method for recording and reproducinginformation on an optical information recording medium according toclaim 1, wherein a tracking system for recording a signal on therecording thin film is a push-pull method.
 3. The method for recordingand reproducing information on an optical information recording mediumaccording to claim 1, wherein a tracking system for reproducing a signalrecorded on the recording thin film is a phase difference trackingmethod.
 4. The method for recording and reproducing information on anoptical information recording medium according to claim 1, wherein whena phase φ₁ of light reflected from the record mark on the opticalinformation recording medium and a phase φ₂ of light reflected from anon-record mark region between the record marks with respect to awavelength λ₂ of incident laser beam for reproduction satisfy arelationship: (2n+0.5)×π<φ₂−φ₁<(2n+1)×π, where n is an integer, a signalis recorded between the grooves of the substrate; and when the followingrelationship is satisfied: (2n+1)×π<φ₂−φ₁<(2n+1.5)×π, where n is aninteger, a signal is recorded on the grooves of the substrate.
 5. Themethod for recording and reproducing information on an opticalinformation recording medium according to claim 1, wherein a value of awavelength λ₂ of the laser beam for reproducing the record mark is 630nm to 670 nm, an interval between the guide grooves is 0.74 μm, a lineardensity of recorded signals is 0.267 μm/bit, and a modulation system ofthe signal is 8/16, RLL (2,10).
 6. The method for recording andreproducing information on an optical information recording mediumaccording to claim 1, wherein in the step of forming the record markbased on an information signal on the recording thin film, at least therecording thin film on which the record mark is to be formed iscrystallized beforehand, and thereafter, the recording thin film isirradiated with laser beam to form the record mark that is amorphous. 7.A method for recording and reproducing information on an opticalinformation recording medium comprising the steps of: irradiating anoptical information recording medium with a laser beam based on aninformation signal while rotating a substrate and moving a laser beamirradiation portion so that an interval between recorded signals in aradial direction is constant, the optical information recording mediumcomprising at least a recording thin film that effects a phase changebetween an amorphous state and a crystalline state by the irradiation ofthe laser beam, the recording thin film formed on a disk-shapedsubstrate including a specular recording region; thereby effecting thephase change to form a record mark on the recording thin film to recorddesired signals at a constant interval in the radial direction; andirradiating the optical information recording medium where the recordmark is formed on the recording thin film with laser beam; therebyreproducing a signal while applying a tracking servo mechanism based ona tracking error signal obtained from the record marks; wherein a valueof a wavelength of the laser beam for reproducing a signal recorded onthe recording thin film is 630 nm to 670 nm, an interval between therecorded signal tracks in the radial direction is 0.74 μm, a lineardensity of recorded signals is 0.267 μm/bit, and a modulation system ofthe signal is 8/16, RLL (2,10).
 8. The method for recording andreproducing information on an optical information recording mediumaccording to claim 7, wherein a tracking system for reproducing a signalrecorded on the recording thin film is a phase difference trackingmethod.
 9. The method for recording and reproducing information on anoptical information recording medium according to claim 7, wherein inthe step of forming the record mark based on an information signal onthe recording thin film, at least the recording thin film on which therecord mark is to be formed is crystallized beforehand, and thereafter,the recording thin film is irradiated with laser beam to form the recordmark that is amorphous.
 10. A method for recording and reproducinginformation on an optical information recording medium, comprising thesteps of: irradiating an optical information recording medium with alaser beam based on an information signal, the optical informationrecording medium comprising at least a recording thin film that effectsa phase change between an amorphous state and a crystalline state by theirradiation of the laser beam, the recording thin film formed on adisk-shaped substrate including guide grooves; thereby recording adesired signal by forming a record mark on the recording thin film whileapplying a tracking servo mechanism with a tracking error signalobtained from the guide grooves of the substrate; and irradiating theoptical information recording medium where the record mark is formed onthe recording thin film with laser beam; thereby reproducing a signalwhile applying a tracking servo mechanism based on a tracking errorsignal obtained from the record mark; wherein when a phase φ₁ of lightreflected from the record mark on the optical information recordingmedium and a phase φ₂ of light reflected from a non-record mark regionbetween the record marks with respect to a wavelength λ₂ of incidentlaser beam for reproduction satisfy a relationship:(2n+0.5)×π<φ₂−φ₁<(2n+1)×π, where n is an integer, a signal is recordedbetween the grooves of the substrate; and when the followingrelationship is satisfied: (2n+1)×π<φ₂−φ₁<(2n+1.5)×π, where n is aninteger, a signal is recorded on the grooves of the substrate.
 11. Themethod of claim 10, wherein a value of a wavelength λ₂ of the laser beamfor reproducing the record mark is 630 nm to 670 nm, an interval betweenthe guide grooves is 0.74 μm, a linear density of recorded signals is0.267 μm/bit, and a modulation system of the signal is 8/16, RLL (2,10).12. The method of claim 10, wherein in the step of forming the recordmark based on an information signal on the recording thin film, at leastthe recording thin film on which the record mark is to be formed iscrystallized beforehand, and thereafter, the recording thin film isirradiated with laser beam to form the record mark that is amorphous.